Dispersion liquid of silica particles and production method therefor

Abstract

Provided is a dispersion liquid of silica particles, comprising silica particles having an average particle diameter of 5 to 300 nm determined from an electron micrograph and a density of 1.20 g/cm3 or more determined from a specific surface area determined by a BET method using nitrogen adsorption, wherein the dispersion liquid has a pH of less than 8, a silica concentration of 12 to 40% by mass, and a viscosity in terms of a silica concentration of 20% by mass of 40 mPa·s or less. When this silica particle is used as an abrasive, it is possible to realize a sufficient polishing speed and a smooth polished surface on which occurrence of scratches is suppressed.

The invention claimed is: 
     
       1. A dispersion liquid of silica particles, comprising silica particles having an average particle diameter of 5 to 300 nm determined from an electron micrograph, and a density of 1.20 g/cm 3  or more and less than 1.60 g/cm 3  determined from the average particle diameter and a specific surface area determined by a BET method using nitrogen adsorption, and an amount of carbon derived from an alkoxy group contained in the silica particles is 0.005% by mass or more and 0.50% by mass or less, wherein the dispersion liquid has a pH of less than 8, a silica concentration of 12 to 40% by mass, and a viscosity in terms of a silica concentration of 20% by mass of 40 mPa-s or less, wherein an amount of a compound containing silicon other than the silica particles in the dispersion liquid is 200 ppm or less, wherein a peak area showing Q4 structure, determined by  29 Si-NMR analysis from −100.0 to −120.0 ppm, is 70% to 90% of a peak area showing Q0 to Q4 structure, determined by  29 Si-NMR analysis from −73.0 to −120.0 ppm. 
     
     
       2. The dispersion liquid of silica particles according to  claim 1 , wherein amounts of the following elements in the dispersion liquid are, per said silica particle, as follows:
 (1) an amount of each of alkali metals, alkali earth metals, Fe, Ti, Zn, Pd, Ag, Mn, Co, Mo, Sn, Al and Zr is less than 0.1 ppm; 
 (2) an amount of each of Cu, Ni and Cr is less than 1 ppb; and 
 (3) an amount of each of U and Th is less than 0.3 ppb. 
 
     
     
       3. The dispersion liquid of silica particles according to  claim 1 , wherein the dispersion liquid comprises ammonia, and a content of ammonia at a silica concentration of 20% by mass is less than 100 ppm. 
     
     
       4. A method for producing a dispersion liquid of silica particles, comprising: preparing a dispersion liquid containing silica particles by using alkoxysilane as raw material; aging by heating the dispersion liquid in the presence of alkali such that a density of the silica particles determined from an average particle diameter determined from an electron micrograph and a specific surface area determined by a BET method using nitrogen adsorption is 1.20 g/cm 3  or more 1.60 g/cm 3  or less, and removing the alkali from the dispersion liquid obtained by aging to once raise a viscosity in terms of a silica concentration of 20% by mass of the dispersion liquid to 60 mPa-s or more and then further removing the alkali to provide a pH of the dispersion liquid of less than 8, wherein an amount of carbon derived from an alkoxy group contained in the silica particles is 0.005% by mass or more and 0.50% by mass or less, an amount of a compound containing silicon other than the silica particles in the dispersion liquid is 200 ppm or less, wherein a peak area showing Q4 structure, determined by  29 Si-NMR analysis from −100.0 to −120.0 ppm, is 70% to 90% of a peak area showing Q0 to Q4 structure, determined by  29 Si-NMR analysis from −73.0 to −120.0 ppm. 
     
     
       5. The method for producing a dispersion liquid of silica particles according to  claim 4 , comprising replacing an organic solvent of the dispersion liquid with water, after preparing the dispersion liquid and before aging the dispersion liquid. 
     
     
       6. The method for producing a dispersion liquid of silica particles according to  claim 4 , wherein the aging is carried out at a pH of 8 or more.